The following invention relates to a fault detector for electrical transmission lines such as buried cables and the like, which detects acoustic energy resulting from a high voltage test pulse arcing to ground at a fault location. Many electrical cables and transmission lines which are buried under the ground develop cracks or faults as a result of rotting or moisture. These faults lead to a short circuit to ground, the location of which is often difficult to detect. In the past, devices have been proposed for the detection of the location of such underground faults using a variety of methods. For example, Williams, U.S. Pat. No. 3,299,351, discloses an electromagnetic field sensing arrangement which compares the phase relationship between the two frequency components of a composite test signal to determine the location of the fault relative to a pair of tuned circuit detectors. A similar device is shown in Link, U.S. Pat. No. 4,039,938. Another device, Pardis, U.S. Pat. No. 4,063,161, locates faults by determining the differences in electrical potential sensed at two locations relative to the fault. A transient surge detector which utilizes a pair of detection units coupled by a radio link is shown in Weintraub, U.S. Pat. No. 2,717,992. All of the aforementioned devices rely upon some type of electromagnetic field detection for determining the location of the fault. Such circuits are either inaccurate due to the difficulty of accurately processing the information at the detection points, or are overly complex if accurate signal processing is to be used.
Another method used in the past to locate faults in buried electrical cable relied upon the fact that when a high voltage pulse reaches a fault location, it arcs to ground, and a noise is sometimes audible, either to the unaided ear or to electronic listening devices. Thus, an electrical pulse generator known as a "thumper" has been used to generate electrical test signals along a cable. The general area of the fault could then be located by listening for the characteristic sound produced by the arcing of the high voltage pulse. This method, however, is useful only for locating the general vicinity of the fault. This is due to the fact that the sound is omnidirectional and diffuses through the earth so that determining the source of the sound is extremely difficult.